Splicing dowel for micropiles and micropiles including such dowels

ABSTRACT

Splicing threaded dowel ( 1 ) for micropiles, characterized in that it includes several adjacent threads with a right or left helix, whose pitch is greater than or equal to 300. Unit shaped by such a dowel ( 1 ) and two micropile sections ( 3 ) with fins ( 7 ). Micropile with helical fins including such a unit.  
     With tightening is obtained the alignment of the fins ( 7 ) of the adjacent sections.

This invention refers to the technical field of foundation piles.

The term “foundation” designates all buried work, which makes up the stable base and course of a structure and distributes the load of this structure onto the undisturbed soil or defers this load onto the undisturbed soil or defers this load onto the bearing hard-soil.

According to the ratio H/B where B is the width of the foundation and H is the course depth, special foundations are distinguished, for those where H/B is less than six, for example for footings and slabs, and deep foundations, for those where H/B is greater than six, for example for separators, wells and piles.

The piles can be classified according to four criteria:

-   -   type of constituent material (wood, metal alloy, concrete among         others);     -   method of introducing into the ground (driving, drilling,         sinking, vibropiling for example);     -   method of transmitting the load (end bearing pile transmitting         only the load by end-bearing effect, friction pile transmitting         only the load by skin friction);     -   size of the piles: according to DTU, a micropile has a diameter         less than 250 mm.

The driven piles are generally made out of steel (profile H with reinforced core or sheet pile) or else made out of precast concrete and are installed by driving with soil back filling.

As an alternative, the driven pile is of the type:

-   -   driven encased: the pile is a metal tube fitted with an         overhanging shoe, a mortar injected through the inside of the         tube, during driving, coming to encase the pile by filling in         the vacuum created by the overhang of the shoe;     -   with driven tube: the pile is made using a metal tube fitted         with a concrete plug, driven into the ground, then filled with         rammed firm concrete (rammed driven pile) or liquid concrete         (molded driven pile).

The sunken piles can be made out of reinforced, precast concrete or concrete placed in a frame at the advanced heading or even made out of steel (profile H with reinforced core or sheet pile) and are installed with soil back filling.

The drilled piles are made of reinforced concrete cast in place in a drill hole.

When the cohesion of the ground allows it, the drilling is carried out without protection (single drilled pile).

In other cases, a metal tube protects the drill hole (cased drilled pile) or a drilling mud is injected (mud-drilled pile).

The drilling is done by auger or rotopercussion.

As an alternative, the drilled pile is of the type:

-   -   molded drilled: the reinforced concrete pile is cast in place in         a drill hole accomplished by using a tool working in rotation;     -   drilled screwed molded: the pile is accomplished by using a         screw tool, sunk in by rotation, fitted with a cast iron plug         that is lost and a tube allowing the concrete to form as the         tool is pulled out little by little.

The driven or drilled piles can be the high-pressure injected type, an injection system composed of tubes with sleeves allowing the injection of a sealing grout into the ground.

It is also known, in the former art:

-   -   of cased molded piles: piles in reinforced concrete cast in         place in a casing tube sunk into the ground;     -   of screw piles: precast piles fitted with a threaded shoe and         sunk in by rotation.

The invention relates for the most part to micropiles.

Micropiles are used for underpinning work, reinforcing the ground (stabilizing slopes or embankments and protecting underground work during excavation projects), and new foundations.

The micropile technique was developed in 1952 by the company, Fondelile, under the direction of the Italian engineer, Lizzi.

These initial piles were drilled and sealed to the ground by a mortar.

These products were used in Italy under the name of “root piles”.

In English, micropiles are called minipiles, micropiles, root piles, needle piles.

They are called mikropfahl, verpresspfahle, wurzelphale in German.

The tables below correspond to the classification of the most current micropiles according the 2002 European Draft Standard CEN TC 288.

According to this European Draft Standard, a micropile is a pile that has a diameter less than 300 mm for piles installed without soil back filling (drilled piles or piles molded in place), and less than 150 mm for piles installed with soil back filling (drilled, water jetted or driven piles).

The first table relates to drilled micropiles. The second table relates to sunken micropiles. Drilling Type of Type of Method Reinforcement Injection Method Grout Options Rotary Concrete Gravitating Grout, Casing drilling reinforcing injection, mortar or Drilling in cage forming concrete concrete Roto Injection in one Grout or percussion single-stroke concrete Clamshell with a temporary bucket casing Bit or plug Load-bearing Gravitating Grout or component injection mortar Injection in one Grout or single-stroke mortar with a temporary casing, a load- bearing component or a tube with sleeves Injection in Grout several strokes with a tube with sleeves Permanent Gravitating Grout, Under- casing (with or injection or mortar or reamed without forming concrete concrete base concrete reinforcing cage Drilling Concrete Forming concrete Grout, with a reinforcing through the mortar or hollow cage hollow rod of concrete continuous the auger auger

Type/ Micropile Options/ Method Material/Casing Section/Reinforcement Injection Precast Steel or cast Full or open tube, Injection reinforced profile-turned around the concrete shaft Closed tube Fill in with grout, mortar or concrete with or without injection around the shaft Molded in Temporary Concrete reinforcing Gravitating place casing cage injection, forming concrete Injection in one single- stroke with a casing Load-bearing Gravitating component injection, forming concrete Injection in one single- stroke with a casing Injection in one single- stroke with a casing with sleeves Injection in several strokes with a casing with sleeves Permanent Concrete reinforcing Dry concrete casing cage forming, with or without underreaming of the base

The invention relates for the most part to foundation micropiles.

They are conventionally designated by the terms micropiles or root pile, piles of modest section, typically with a diameter less than 250 mm, installed with tooling of reduced size, light and easy to handle, in particular for underpinning work.

Because of their low diameter, micropiles do not work in toe, their bearing depending in essence on side friction.

Conventional micropiles are of four different types (DTU 13-2, 1978, modified by 1991 additional clause and resumption in the LCPC's Fascicle 62-Title V dating back to 1993):

-   -   type I: cased drilled pile with a diameter less than 250 mm. The         drill hole is equipped with or without reinforcements and filled         in with a cement mortar by means of a tremie. The casing is         recovered by blocking it off at the head and putting it under         pressure on top of the mortar. The root piles of the company,         Fondelile, were of this category;     -   type II: drilled pile, with a diameter less than 250 mm, with         gravitating injection without pressure. The drill hole is         equipped with reinforcement and filled in with a sealing grout         or mortar, through gravity or under very low pressure, by means         of a tremie. When the nature of the soil allows it, drilling can         be replaced with water jetting, driving or sinking;     -   type III: drilled pile, with a diameter less than 250 mm, with         total unit injection under IGU pressure. The drill hole is         equipped with reinforcements and an injection system that is a         tube with sleeves installed in a sheathing grout. If the         reinforcement is a metal tube, this tube can be equipped with         sleeves and take the place of an injection system. This         injection is performed at the head, overall and by unit, at a         pressure greater than or equal to 1 MPa. When the nature of the         soil allows it, drilling can be replaced by water jetting,         driving or sinking;     -   type IV: drilled pile, with a diameter less than 250 mm, with         repetitive and selective injection under IRS pressure. The drill         hole is equipped with reinforcements and an injection system         that is a tube with sleeves installed in a sheathing grout. If         the reinforcement is a metal tube, this tube can be equipped         with sleeves and take the place of an injection system. This         injection is performed at the single or double plug of a sealing         grout or mortar at an injection pressure greater than or equal         to 1 MPa.

The micropiles are used for:

-   -   stabilizing existing foundations that settle, for example on         individual detached homes after soil drought, flooding or         defective work;     -   reinforcing these existing foundations that must take on         additional load;     -   supporting the load of the structure on sites where access is         exiguous (rehabilitation);     -   build foundations in hard soils, go through old masonries         without trepanning or excessive vibrations bringing about         damages to existing work.

Micropiles are conventionally grouted to the work either by sealing to the anti-shrinking mortar, in the existing foundations, or by an embedded distribution plate in a reinforced concrete header joist.

The drilled micropiles are used quite often for underpinning work in a compact space, in the case of individual habitats among others.

Micropiles are also used in groups (unit of vertical micropiles) or in networks (unit of vertical and inclined micropiles) to reinforce the ground soils.

Document EP-0.954.645, in the name of Target Fixings, describes a pile containing multiple outer helical fins, practically along the entire length of the pile, this pile having an outside diameter of at least 25 mm, at least one of the fins having a wedged-shaped cross-section. After creating a pre-drilled-hole, the pile is installed by driving with a hydraulic or pneumatic hammer, the fins of the pile triggering its rotation into the ground, during the driving. No injection of binder is done or possible at the time the pile is installed described in the EP-0.954.645 document, this pile being massive, for example molded, or even hollow but closed and filled with a material such as resin or polymer material, before being installed into the ground.

The claimant has developed micropiles with inner cores, injectable or not, having noticed that the piles described in the document EP-0.954.645 do not make it possible to reach withdrawal resistance required in certain applications

The creation of micropile with a massive axial core confers to the pile an increased resistance to buckling, contrary for example to the pile described in the 1943 document U.S. Pat. No. 2,232,990.

The micropiles of the claimant are installed by sinking in components of roughly one meter in length; these components are made of cast aluminum.

The assembly of components is done by using a stainless steel dowel.

The geometry of micropiles of the claimant is such that they screw themselves into the ground, under the reaction of a hammer, without vibrating, and this by compressing the surrounding soil.

The claimant has however noticed that the micropile components can be not properly positioned one in relation to the other. The claimant has noticed that this problem was present in other micropiles, conventional, assembled by dowels.

The tightening by hand at assembly of micropile components is followed by an uncontrolled tightening at the time the micropiles are sunk in, because of the striking and vibrations. The higher component can act like an impact wrench and the tightening continues, in such a way that the helical edges of the micropile components are not placed in continuity.

The invention aims to mitigate this problem.

For this purpose, the invention is referred, according to an initial aspect, to a threaded splicing dowel for micropiles, including several adjacent threads with a right or left helix, whose pitch is greater than or equal to 300.

This dowel exhibits, depending on various creations, the following characteristics, combined if need be:

-   -   it includes three symmetrical buttress threads;     -   its diameter is less than 30 mm, and is valid in particular for         16 and 24 mm, the pitch being 300, 600, 900 or 1200;     -   it is made out of stainless steel, in particular austenitic         stainless steel 1.4404;     -   it is provided with a anti-corrosive coating, in particular         epoxy paint applied hot;     -   it is provided furthermore with a coating facilitating the         sliding against the threads, in particular         polytetrafluorethylene film.

The invention refers, according to a second aspect, to a unit shaped by a dowel such as presented above, and two micropile sections including each at least one fin, the micropile sections including each one axial tapping emerging on the right of a crosswise bearing surface, the sum of the boring lengths of these tappings being greater than the length of the dowel.

Advantageously, the axial tappings of the two sections are virtually identical.

Advantageously, the boring of tappings is 76.5 mm, the tappings extending over 64.5 mm, the overall length of the dowel being 144 mm, the length of the threading on the dowel being 120 mm, the dowel protruding like this in relation to the crosswise bearing plane of one of the sections over a 55.5 mm length of threads when it is screwed all the way into the tapping of this section.

The invention refers, according to a third aspect, to a micropile including at least one unit such as presented above, the sections of this micropile being made out of cast aluminum.

Other objects and advantages of the invention will appear during the course of the following description of currently preferred creation methods, description that will be carried out while referring to the drawings appended in which:

FIG. 1 is a side view of a threaded dowel installed in a micropile component, according to a creation method of the invention;

FIG. 2 is an angle view of two helical micropile segments ready to be assembled one to the other by a threaded dowel as represented in FIG. 1.

The dimensions that are going to be specified below should not be seen as limiting of the invention, but as an illustration of currently preferred creation methods of the invention.

The dowel 1 represented in FIG. 1 is screwed by hand into an axial tapping 2 of a micropile section 3.

Advantageously, for a micropile formed by assembling sections 3 using dowels 1, all the dowels 1 are virtually identical and are screwed into identical tappings.

As an example, the boring is 76.5 mm, the tapping being 64.5 mm, the overall length of the dowel being 144 mm, the length of the threading on the dowel being 120 mm. When the dowel is screwed in by hand all the way to the thread, it protrudes like this a 55.5 mm length of threads, the tolerance being more or less 1 mm.

Advantageously, the pitch of the threading is fine and 1200, in such a way that when a section carries out a turn of thread on the splicing dowel, the two crosswise bearing faces 4, 5 of the sections move away or come together from one another by 12 mm.

In other creation methods, the pitch of the threading is 300, 600 or 900.

By “pitch” it is designated here the distance measured in a plane containing the axis of the threaded mechanical part, between two points equivalent to two successive profiles in one same thread.

In the creation method represented in FIG. 1, the pitch of the helix is on the right. This helix pitch will be chosen in such a way as the screwing of the micropiles into the ground, at the time of sinking them in, leads to a tightening of the micropile sections.

Advantageously, the threads 6 are three in numbers.

In the creation method of FIG. 1, three buttress threads are used. Starting to bore the dowel into the tapping is always done by the three threads at the same time. As an indication, the diameter of the dowels 1 is for example 16 mm or 24 mm.

With the dimensions indicated prior to that, at the time of the tightening by hand of the micropile sections, it is possible to put the helical fins 7 of the micropile sections slightly at 12° from one another. At the time the micropile is sunken in, by self-tightening, the fins come together in perfect alignment.

The micropile sections being made out of cast aluminum, the dowels are advantageously made of stainless steel, for example type 1.4404 (austenitic stainless steel AISI 316L).

To avoid corrosion and galvanic coupling, a protective coating is applied on the dowels. In a creation, this coating is an epoxy paint applied hot. In an advantageous creation, a Teflon® film is applied, for example by spraying, on the dowel coated with epoxy paint. 

1. A threaded dowel for micropiles, comprising several adjacent threads with a right or left helix, the threads having a pitch which is greater than or equal to
 300. 2. Dowel according to claim 1, wherein the threads include three symmetrical buttress threads.
 3. Dowel according to claim 2, wherein the diameter of the dowel is less than 30 mm.
 4. Dowel according to claim 1, wherein the dowel is made out of stainless steel.
 5. Dowel according to claim 4, wherein the dowel is provided with an anti-corrosive coating.
 6. Dowel according to claim 5, wherein the dowel is provided furthermore with a coating facilitating sliding against the threads.
 7. A unit shaped and configured to threadingly receive the dowel according to claim 1, the unit comprising two micropile sections each including at least one fin, wherein the micropile sections each include one axial tapping emerging on the right of a crosswise bearing surface, the sum of the boring lengths of these tappings being greater than the length of the dowel.
 8. Unit according to claim 7, wherein the axial tappings of the two sections are identical.
 9. Unit according to claim 7, wherein the boring of tappings is 76.5 mm, the tappings extend over 64.5 mm, the overall length of the dowel is 144 mm, the length of the threading on the dowel is 120 mm, and the dowel protruding in relation to the crosswise bearing plane of one of the sections over a 55.5 mm length of threads when the dowel is screwed all the way into tapping of this section.
 10. A micropile including at least one unit according to claim 7, wherein sections of the micropile are made out of cast aluminum.
 11. Dowel according to claim 4, wherein the dowel is made of austenitic stainless steel 1.4404.
 12. Dowel according to claims 5, wherein the anti-corrosive coating is a hot-applied epoxy paint.
 13. Dowel according to claim 6, wherein the coating facilitating sliding is a polytetrafluorethylene film. 